The present invention relates to glass compositions, and more particularly to novel lead-free U.V. absorbing glass compositions. While the compositions of the present invention have particular utility in the compounding of inks such as silk screen inks to provide a U.V. absorbing glaze or enamel, they have utility in any application requiring a U.V. absorbing glass, including protective eyewear and the like.
There are a wide variety of applications in which a thin glaze or enamel of U.V. absorbing glass is deposited on part or all of a base glass substrate to prevent the transmission of ultraviolet light (in general the term "glaze" being understood to mean a transparent glass, while an "enamel" will be understood to mean a glass containing pigment or other particles in suspension). For example, in the fabrication of motor vehicles, particularly in the sealing of glass windshields and the like, materials are employed which tend to be very sensitive to ultraviolet light. In order to protect these sealant materials it is common practice to deposit a thin narrow strip of ultraviolet light absorbing enamel at the peripheral edges of such automotive glass to prevent transmission of potentially harmful U.V. radiation to the sealant.
While the discussion which follows will refer to "windshields" and/or "windshield glass", it will be understood that unless otherwise clear from the context, these terms will be understood to refer to any automotive glass member, i.e. windshield, rear window, side windows, etc.
At the present time, these enamels are typically compounded from a lead oxide containing glass composition, which is suspended, together with a black pigment, in a suitable vehicle to provide an ink which can be silk screened onto the edges of the automotive windshield. In this way, during final shaping of the windshield member, the enamel or glaze can be fired, fusing it with the windshield to provide a thin layer of glass, typically about 0.25 to 2 inches wide and about 1 mil in thickness.
The glass compositions presently employed in such application typically do not have sufficient U.V. absorption characteristics to be employed as a glaze, and therefore are normally used in conjunction with a black pigment to provide an enamel having substantially better U.V. absorbing characteristics than the glass alone.
In his work entitled "Coloured Glasses" (Society of Glass Technology, 1951 Reprint 1967, pages 212-213 and 232-234) Weyl discusses the use of metal oxide mixtures glass. In the course of his discussion, Weyl notes that mixtures of TiO.sub.2 with Fe.sub.2 O.sub.3 or CeO.sub.2 can promote a shift in the iron or cerium valence, thereby shifting the light wave length absorbed by the glass. He specifically suggests that cerium oxide may impart U.V. light absorbing characteristics to lead glasses.
It will, of course, be understood that it is highly desirable to provide a glass having improved ultraviolet light absorbing characteristics. It will be equally apparent that it would be particularly advantageous to obtain such improved U.V. properties in a glass which was lead free, so as to provide greater safety by elimination of lead from both the work place in which the glass compositions are prepared and used as well as the final glass composition itself.